A facile method to obtain colloidal dispersions of nickel hydroxide: improving the processing of nickel oxide and facilitating its upscaling for perovskite-type solar devices.

Nickel hydroxide has been successfully employed as a precursor to the widely used, inorganic hole transport material (HTM) nickel oxide (NiOx). However, manufacturing NiOx HTM layers from nickel hydroxide is more complicated than those involving organometallic precursors due to its poor solubility/dispersibility. We report here a substantial increase in nickel hydroxide dispersibility in organic solvents by complexing it with monoethanolamine. These improvements have enabled us to develop a simpler method for processing nickel hydroxide that resemble the known sol-gel method. The new metal complex remains dispersed for months and converts to nickel oxide at a temperature similar to that of nickel hydroxide (270-300 ºC). An extensive characterisation of NiOx films obtained from the deposited precursor has been carried out. Perovskites solar cells have also been built with these films as a proof of concept, showing promising results for the layers sintered at low (270 ºC) and high (500 ºC) temperatures. The pixel with highest efficiency for both sintering temperatures were 14.7% and 16.7%, respectively, which are close to or surpass the ones of the control samples (15.4% and 15.7%, respectively). The applied unpaired t-test statistical method showed that the mean efficiency values for our thick samples prepared at 270oC are not statistically different from those of the control cells. Furthermore, the samples prepared at 500oC presented a significant statistical difference with the control cells, showing higher average efficiencies (12.8% and 13.3% versus 11.4% and 11.7%, reverse and forward measurements, respectively). The simplicity of the manufacturing method developed, together with the use of non-toxic organic compounds for its preparation and the promising results observed in solar devices, makes it suitable for being upscaled.